Thermoplastic polyurethanes have been long known, and are used in a wide range of fields including elastomer fibers, elastomers, artificial leathers, and coating compositions. In general, thermoplastic polyurethane resins are obtained by reacting either a polyether diol, such as poly(propylene glycol) having a molecular weight of from 500 to 4,000, a mixed polypropylene-polyethylene glycol or poly(tetramethylene ether glycol, or a polyester glycol, such as poly(butylene adipate) or poly(caprolactone glycol)), an organic diisocyanate and a chain extender such as a short-chain glycol and a short-chain diamine. Examples of the organic diisocyanate include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and 1,6-hexane diisocyanate (HDI). Examples of the short-chain glycol and short-chain diamine chain extenders include 1,4-butanediol, 1,6-hexanediol, ethylenediamine, propylenediamine, 4,4'-diaminodiphenylmethane, and methylenebismonochloroaniline. In these thermoplastic polyurethane resins, the long-chain diol provides soft segments, while the segments formed from the organic diisocyanate and the short-chain glycol and short-chain diamine chain extenders serve as hard segments. As a result, the resins have a microscopically phase-separated structure to exhibit rubber elasticity. By changing the kinds and proportions of the long-chain diol, organic diisocyanate, and chain extenders used, various rubbery properties can be obtained according to use purposes and various desired performances.
In recent years, however, higher functions are desired increasingly with the expansion of the range of applications of thermoplastic polyurethane resins. Especially strongly desired is a thermoplastic polyurethane having excellent heat resistance and excellent low-temperature properties, i.e., a thermoplastic polyurethane resin having a broad rubbery-state region. Conventional thermoplastic polyurethanes lose their elasticity at around 120.degree. C. Generally employed for improving heat resistance are a technique of increasing the proportion of a diisocyanate and a chain extender and a technique of using as an additional chain extender a polyol or a polyamine each having a functionality of 3 or higher. Although these techniques are effective in improving heat resistance, the polyurethane resins obtained not only have reduced rubber elasticity but also tend to lose thermoplasticity. On the other hand, a thermoplastic polyurethane having rubber elasticity at temperatures up to around 200.degree. C. is disclosed in JP-A-3-177413, which polyurethane is obtained using as a chain extender a specific diol compound containing a spiro ring. (The term "JP-A" as used herein means an "unexamined published Japanese patent application.") This prior art polyurethane has improved heat resistance and is suitable for use in applications where heat resistance is required. However, the proposed polyurethane cannot be an effective elastomer at a temperature of 0.degree. C. and lower because it has an increased modulus of elasticity at such a low temperature.